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Recent attention in the biomedical and orthopedic sectors has been drawn towards bone defects, emerging as a prominent focus within orthopedic clinics. Hydrogels, due to their biocompatibility, elevated water content, softness, and flexibility, are increasingly acknowledged in tissue regeneration research. Advanced biomaterials offer numerous advantages over traditional materials, notably the capacity to respond to diverse physical, chemical, and biological stimuli. Their responsiveness to environmental cues, such as three-dimensional (3D) morphology and phase conditions, holds promise for enhancing the efficacy of localized bone lesion repairs. This paper aims to revolutionize the treatment of severe bone abnormalities by providing a comprehensive examination of hydrogels capable of morphological adaptation to environmental changes. It delineates their classification, manufacturing principles, and current research status within the field of bone defect regeneration. [ABSTRACT FROM AUTHOR]

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Herein, a novel 3D printable ink designed for the fabrication of interpenetrating polymer network (IPN) hydrogels is introduced, ingeniously integrating a polyelectrolyte complex (PEC) of hyaluronic acid (HA) and chitosan (CS) with a photo‐crosslinkable P(OEGMA‐co‐EGDEMA) polymer. Initially, the carboxyl group of HA is modified with a photo‐labile ortho‐nitrobenzyl group, preventing premature PEC formation during 3D ink formulation. Subsequent UV illumination via digital light processing (DLP) simultaneously triggers the photo‐deprotection of the carboxyl group of HA and the photopolymerization of OEGMA crosslinked hydrogel, together creating a PEC‐integrated IPN hydrogel. Comprehensive characterizations, including NMR, IR, UV/Vis, TGA, DSC, SEM, and mechanical tests are conducted to evaluate the structural, morphological, and rheological properties of these hydrogels. Furthermore, adjustments to the composition of the 3D ink enable the production of hydrogels with a spectrum of mechanical strength and elastic modulus ranging from 1 to 10 kPa. The resultant PEC‐IPN hydrogels display excellent flexibility, compressive strength, high strain tolerance, pH responsiveness, and thermal stability. In essence, the approach seamlessly merges natural polyelectrolytes with technological innovation to refine 3D ink production. This method could mark a pivotal advancement in the realm of 3D materials, unlocking numerous prospective applications. [ABSTRACT FROM AUTHOR]

Biomedicine is constantly evolving to ensure a significant and positive impact on healthcare, which has resulted in innovative and distinct requisites such as hydrogels. Chitosan-based formulations stand out for their versatile utilization in drug encapsulation, transport, and controlled release, which is complemented by their biocompatibility, biodegradability, and non-immunogenic nature. Stimuli-responsive hydrogels, also known as smart hydrogels, have strictly regulated release patterns since they respond and adapt based on various external stimuli. Moreover, they can imitate the intrinsic tissues' mechanical, biological, and physicochemical properties. These characteristics allow stimuli-responsive hydrogels to provide cutting-edge, effective, and safe treatment. Constant progress in the field necessitates an up-to-date summary of current trends and breakthroughs in the biomedical application of stimuli-responsive chitosan-based hydrogels, which was the aim of this review. General data about hydrogels sensitive to ions, pH, redox potential, light, electric field, temperature, and magnetic field are recapitulated. Additionally, formulations responsive to multiple stimuli are mentioned. Focusing on chitosan-based smart hydrogels, their multifaceted utilization was thoroughly described. The vast application spectrum encompasses neurological disorders, tumors, wound healing, and dermal infections. Available data on smart chitosan hydrogels strongly support the idea that current approaches and developing novel solutions are worth improving. The present paper constitutes a valuable resource for researchers and practitioners in the currently evolving field. [ABSTRACT FROM AUTHOR]

Iron nanoparticles were prepared by using the co-precipitation process, and then used to fabricate magnetic field-responsive hydrogel films. The magnetic nanoparticles' structural, physical-chemical, morphological, and magnetic characteristics and the effect of hydrogel films' coating concentration were studied. The properties of the hydrogel film responsive to the magnetic field were investigated using Fourier analysis spectroscopy infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and a vibration sample magnetometer (VSM). The results indicated that all samples showed good inter-integration of the constituent materials and their functional groups. The hydrogel film samples which were polycrystalline, had broad diffraction peaks and showed constant particle size with nearly spherical particles with rounded edges. The SEM image of the magnetic nanoparticles with and without coating was established for the accumulation of numerous nanoparticles with a 17 nm mean diameter. In addition, the magnetic properties of the magnetic field-sensitive hydrogel films were evident and sufficient for drug delivery to the desired location.

Hydrogels are among the most promising materials for biological applications mainly because of their ability to absorb large volumes of water and carry as well as deliver biologically active substances. A challenge is to make them appropriately responsive to environmental triggering factors simply and reliably. In this work, we present a basic approach of modification of a commonly used, low-cost poly (acrylic acid) – PAA – hydrogel with biocompatible surfactants regarding their possible thermoresponsive activity.Viscoelasticity, hydration, and molecular diffusion processes, in relation to the morphology of the hydrogel and its mixture with nonionic surfactant Brij 58, are studied systematically using oscillatory rheometry, NMR diffusiometry and imaging, and cryoSEM. Our results contribute to the understanding of interactions between weak PAA and nonionic surfactants. The changes of the hydrogel microstructure caused by nonionic and bio-safe surfactant or thermal induction are clearly reflected in their mechanical response as well as the translational mobility of water molecules entrapped within the hydrogel's network. The structural modification induced by adding nonionic surfactant gives rise to a decrease in hydrogel elasticity.

Hydrogels represent three-dimensional, interconnected networks known to absorb substantial amounts of H2O but at the same time, being insoluble in the aforementioned solvent. Their exceptional hydrophilic nature, biocompatibility and diverse therapeutic potential position them as highly promising biomaterials within biological and biomedical fields. These materials, on account of their innoxious innate characteristics and safe utilization, have garnered widespread acceptance across tremendous and diverse biomedical applications ranging from traditional therapies to state-of-the-art advancements. This extensive review incorporates a spectrum of varied types of hydrogels, elaborating on both their chemical, physical aspects and also throws light on the rheological, analytical and spectroscopic tools employed for their characterization. It also continues to elaborate on the various mechanisms of gelation for facilitating a better understanding of the topic under discussion. The review also discusses the different strategies which are substantiated in recent times to expand the utilisation of hydrogels. The primary intent of this review is to render a comprehensive understanding of hydrogels as an ideal drug delivery system to undergraduates, graduates, biomedical students and researchers across the globe. It also targets to unravel the fundamental, applied and general aspects of hydrogels, offering valuable insights to help individuals associated with multidisciplinary research and application spheres. [ABSTRACT FROM AUTHOR]

Low utilization of solar energy remains a challenge that limits photocatalytic efficiency. To address this issue, this work proposes a bionic solar photocatalytic reactor (BSPR) for efficient selective oxidation of aromatic alcohols. A biomimetic phototropic hydrogel is prepared by coupling chlorine‐doped polypyrrole (Cl‐PPy) and poly(N‐isopropyl acrylamide) (PNIPAm) to maximize light‐harvesting efficiency automatically, allowing the BSPR to maintain high catalytic levels throughout the day. Molecular dynamics simulations are used to unveil the understanding of the fast photoresponsive behavior of Cl‐PPy/PNIPAm from a molecular level, while COMSOL simulations are conducted to follow the macroscopically phototropic mechanism of BSPR. Attributing to the existence of PdS/S vacancies riched ZnIn2S4 nanocomposite in the top flower‐shaped hydrogel, the BSPR displays a special function for efficiently photocatalytic oxidation of aromatic alcohols under solar illumination (yield of 4‐methoxybenzaldehyde: 479.5 µmol g−1 h−1; selectivity: 68.8%). Two possible reaction pathways are identified as follows: photogenerated holes can attract aromatic alcohols directly and generate aromatic aldehydes; photoexcited electrons oxidize O2 to ·O2− can also react with the adsorbed aromatic alcohol. This study presents a promising paradigm that explores opportunities for enhanced utilization of light energy, offering a novel approach to maximize its efficiency in practical applications. [ABSTRACT FROM AUTHOR]

The repair of irregular bone tissue suffers severe clinical problems due to the scarcity of an appropriate therapeutic carrier that can match dynamic and complex bone damage. Fortunately, stimuli-responsive in situ hydrogel systems that are triggered by a special microenvironment could be an ideal method of regenerating bone tissue because of the injectability, in situ gelatin, and spatiotemporally tunable drug release. Herein, we introduce the two main stimulus-response approaches, exogenous and endogenous, to forming in situ hydrogels in bone tissue engineering. First, we summarize specific and distinct responses to an extensive range of external stimuli (e.g., ultraviolet, near-infrared, ultrasound, etc.) to form in situ hydrogels created from biocompatible materials modified by various functional groups or hybrid functional nanoparticles. Furthermore, “smart” hydrogels, which respond to endogenous physiological or environmental stimuli (e.g., temperature, pH, enzyme, etc.), can achieve in situ gelation by one injection in vivo without additional intervention. Moreover, the mild chemistry response-mediated in situ hydrogel systems also offer fascinating prospects in bone tissue engineering, such as a Diels–Alder, Michael addition, thiol-Michael addition, and Schiff reactions, etc. The recent developments and challenges of various smart in situ hydrogels and their application to drug administration and bone tissue engineering are discussed in this review. It is anticipated that advanced strategies and innovative ideas of in situ hydrogels will be exploited in the clinical field and increase the quality of life for patients with bone damage.

Additive manufacturing (AM) aka three-dimensional (3D) printing has been a well-established and unparalleled technology, which is expanding the boundaries of materials science and is exhibiting an enormous potential to fabricate intricate geometries for healthcare, electronics, and construction sectors. In the contemporary era, the combination of AM technology and stimuli-responsive hydrogels (SRHs) helps to create dynamic and functional structures with extreme accuracy, which are capable of changing their shape, functional, or mechanical properties in response to environmental cues such as humidity, heat, light, pH, magnetic field, electric field, etc. 3D printing of SRHs permits the creation of on-demand dynamically controllable shapes with excellent control over various properties such as self-repair, self-assembly, multi-functionality, etc. These properties accelerate researchers to think of unthinkable applications. Additively manufactured objects have shown excellent potential in applications like tissue engineering, drug delivery, soft robots, sensors, and other biomedical devices. The current review provides recent progress in the 3D printing of SRHs, with more focus on their 3D printing techniques, stimuli mechanisms, shape-morphing behaviors, and their functional applications. Finally, current trends and future roadmap of additively manufactured smart structures for different applications have also been presented, which will be helpful for future research. This review holds great promise for providing fundamental knowledge about SRHs to fabricate structures for diverse applications.

Abstract This comprehensive review delves into a unique intersection of hydrogels as smart molecules and their transformative applications in ophthalmology. Beginning with the foundational definition, properties, and classification of hydrogels, the review explores their synthesis and responsive capabilities. Specific applications examined encompass topical drug delivery, contact lenses, intravitreal drug delivery, ocular adhesives, vitreous substitutes, and cell‐based therapy. A methodical analysis, including an overview of relevant ocular structures and a comparative evaluation of hydrogel‐based solutions against traditional treatments, is conducted. Additionally, potential constraints, translation challenges, knowledge gaps, and research areas are identified. Our methodical approach, guided by an extensive literature review from 2017 to 2023, illuminates the unprecedented opportunities offered by hydrogels, along with pinpointing areas for further inquiry to facilitate their transition into clinical practice.

Postoperative peritoneal adhesions occur in the majority of patients undergoing intra-abdominal surgery and are one of the leading causes of hospital re-admission. There is an unmet clinical need for effective anti-adhesive biomaterials, which can be applied evenly across the damaged tissues. We examined three different responsive hydrogel types, i.e. a thermosensitive PLGA-PEG-PLGA, a pH responsive UPy-PEG and a shear-thinning hexapeptide for this purpose. More specifically, their potential to be homogeneously distributed in the peritoneal cavity by high pressure nebulization and prevent peritoneal adhesions was evaluated. Solutions of each polymer type could be successfully nebulized while retaining their responsive gelation behavior in vitro and in vivo. Furthermore, none of the polymers caused in vitro toxicity on SKOV3-IP2 cells. Following intraperitoneal administration, both the PLGA-PEG-PLGA and the hexapeptide hydrogels resulted in local inflammation and fibrosis and failed in preventing peritoneal adhesions 7 days after adhesion induction. In contrast, the pH sensitive UPy-PEG formulation was well tolerated and could significantly reduce the formation of peritoneal adhesions, even outperforming the commercially available Hyalobarrier® as positive control. To conclude, local nebulization of the bioresponsive UPy-PEG hydrogel can be considered as a promising approach to prevent postsurgical peritoneal adhesions. [Display omitted] [ABSTRACT FROM AUTHOR]

Wound management represents a well-known continuous challenge and concern of the global healthcare systems worldwide. The challenge is on the one hand related to the accurate diagnosis, and on the other hand to establishing an effective treatment plan and choosing appropriate wound care products in order to maximize the healing outcome and minimize the financial cost. The market of wound dressings is a dynamic field which grows and evolves continuously as a result of extensive research on developing versatile formulations with innovative properties. Hydrogels are one of the most attractive wound care products which, in many aspects, are considered ideal for wound treatment and are widely exploited for extension of their advantages in healing process. Smart hydrogels (SHs) offer the opportunities of the modulation physico-chemical properties of hydrogels in response to external stimuli (light, pressure, pH variations, magnetic/electric field, etc.) in order to achieve innovative behavior of their three-dimensional matrix (gel–sol transitions, self-healing and self-adapting abilities, controlled release of drugs). The SHs response to different triggers depends on their composition, cross-linking method, and manufacturing process approach. Both native or functionalized natural and synthetic polymers may be used to develop stimuli-responsive matrices, while the mandatory characteristics of hydrogels (biocompatibility, water permeability, bioadhesion) are preserved. In this review, we briefly present the physiopathology and healing mechanisms of chronic wounds, as well as current therapeutic approaches. The rational of using traditional hydrogels and SHs in wound healing, as well as the current research directions for developing SHs with innovative features, are addressed and discussed along with their limitations and perspectives in industrial-scale manufacturing. [ABSTRACT FROM AUTHOR]

The scientific community has widely recognized thermosensitive hydrogels as highly biocompatible material with immense potential in drug delivery systems. When the temperature of these hydrogels approaches that of human body, a phase change occurs, enhancing their usefulness in a range of medical scenarios. This review article highlighted the background of thermosensitive hydrogels, their properties, and their applications in transdermal, oral, ophthalmic, intravaginal, nasal, rectal, cancer therapy, and cell‐loaded drug delivery systems. The literature suggests numerous advantages of these hydrogels over conventional drug delivery systems and find applications in various fields, such as therapeutic systems, filling processes, and sustained drug delivery systems. One of their key benefits is the ability to eliminate invasive procedures like surgery, providing a noninvasive alternative for drug administration. Moreover, they streamline the formulation process for both hydrophilic and hydrophobic drug delivery systems, simplifying the development of effective treatments. The thermosensitive hydrogels have been found to be green materials with negligible side effects and desirable drug delivery properties. The thermosensitive hydrogel's sustained‐release characteristics, immunogenicity, and biodegradability have also gained increased interest. Some of the disadvantages of thermosensitive hydrogels include delayed temperature response, weak mechanical characteristics, and poor biocompatibility, which limits their potential use in drug delivery applications. [ABSTRACT FROM AUTHOR]

Nature utilizes non-equilibrium self-assembly to achieve remarkable functions. Although such systems have been synthesized, this class of assembly is only sparsely explored in innovative materials with life-like functions. Here, we report transient nanoparticles driven by adenosine triphosphate and their applications on the self-erasable and rewritable security labels. We show that the lifetime of transient nanoparticles can be tuned from a few minutes to hundreds of minutes through adjusting concentrations of the components. By integrating the transient nanoparticles into hydrogels, we achieve self-erasable and rewritable labels with time- and space-encoded information encryption. Notably, a smart Morse code is implemented by programming the hydrogel labels in a spatiotemporal manner. This work provides an emerging material involving transient nanoparticles for information encryption, further accelerating the explorations of the new type information encryption materials. [ABSTRACT FROM AUTHOR]

The common techniques to improve hydrogel's mechanical properties include increasing crosslinking density and forming crosslinked double‐network hydrogel, which may cause some hydrogels to lose their smart functionalities. Inspired by entanglement‐induced strengthening, a simple approach to introducing hydroxypropyl cellulose (HPC) fibers entangled with different smart hydrogel matrix systems are reported. Different from the conventional methods which hinder the movement of the polymer network, through entanglement with HPC fibers, the composite hydrogel shows both improved Young's modulus and toughness and more importantly improved smart functionalities including response speed, anti‐drying, and anti‐freezing capabilities and cycle stability. This strategy provides a new design rule to fabricate durable and strengthened smart hydrogels which can be used in smart windows, sensors, and soft robots. [ABSTRACT FROM AUTHOR]

Hydrogels are promising ultrasound-responsive drug delivery systems. In this study, we investigated how different ultrasound parameters affected drug release and structural integrity of self-healing hydrogels composed of alginate or poloxamers. The effects of amplitude and duty cycle at low frequency (24 kHz) ultrasound stimulation were first investigated using alginate hydrogels at 2% w/v and 2.5% w/v. Increasing ultrasound amplitude increased drug release from these gels, although high amplitudes caused large variations in release and damaged the gel structure. Increasing duty cycle also increased drug release, although a threshold was observed with the lower pulsed 50% duty cycle achieving similar levels of drug release to a continuous 100% duty cycle. Poloxamer-based hydrogels were also responsive to the optimised parameters at low frequency (24 kHz, 20% amplitude, 50% duty cycle for 30 s) and showed similar drug release results to a 2.5% w/v alginate hydrogel. Weight loss studies demonstrated that the 2% w/v alginate hydrogel underwent significant erosion following ultrasound application, whereas the 2.5% w/v alginate and the poloxamer gels were unaffected by application of the same parameters (24 kHz, 20% amplitude, 50% duty cycle for 30 s). The rheological properties of the hydrogels were also unaffected and the FTIR spectra remained unchanged after low frequency ultrasound stimulation (24 kHz, 20% amplitude, 50% duty cycle for 30 s). Finally, high-frequency ultrasound stimulation (1 MHz, 3 W.cm−2, 50% duty cycle) was also trialled; the alginate gels were less responsive to this frequency, while no statistically significant impact on drug release was observed from the poloxamer gels. This study demonstrates the importance of ultrasound parameters and polymer selection in designing ultrasound-responsive hydrogels. [ABSTRACT FROM AUTHOR]

Wearable bioelectronics and therapeutics are a rapidly evolving area of research, with researchers exploring new materials that offer greater flexibility and sophistication. Conductive hydrogels have emerged as a promising material due to their tunable electrical properties, flexible mechanical properties, high elasticity, stretchability, excellent biocompatibility, and responsiveness to stimuli. This review presents an overview of recent breakthroughs in conductive hydrogels, including their materials, classification, and applications. By providing a comprehensive review of current research, this paper aims to equip researchers with a deeper understanding of conductive hydrogels and inspire new design approaches for various healthcare applications. [ABSTRACT FROM AUTHOR]

Smart hydrogels have been known for their remarkable applications in various fields of research. Among these smart hydrogels, magnetically responsive hydrogels are more famous because of the ease of their manipulation and a much quicker magnetic response. However, many magnetic hydrogels exhibit fragile and brittle properties. In this study, a smart combination of salting‐out and cyclic freezing–thawing was utilized for the first time to deal with sodium alginate/polyvinyl alcohol based magnetic hydrogel. The optimized magnetic hydrogel has outstanding mechanical properties with 6.66 MPa at the elongation at break of 282%, Young's modulus of 2.51 MPa, and worked with extension at fracture Wext of 9.31 MJ m−3. The magnetic hydrogel could be easily controlled by magnet, such as swim freely in water when controlled by three‐dimensional electromagnetic field. All the results show that these newly fabricated magnetic hydrogel can also carry out many difficult tasks in terms of magnetic response mechanics. This type of tough and magnetically responsive hydrogels can be used for numerous applications such as in swimming robots, flexible gripper, bionic of natural cartilage. [ABSTRACT FROM AUTHOR]

Abstract The scientific community has widely recognized thermosensitive hydrogels as highly biocompatible material with immense potential in drug delivery systems. When the temperature of these hydrogels approaches that of human body, a phase change occurs, enhancing their usefulness in a range of medical scenarios. This review article highlighted the background of thermosensitive hydrogels, their properties, and their applications in transdermal, oral, ophthalmic, intravaginal, nasal, rectal, cancer therapy, and cell‐loaded drug delivery systems. The literature suggests numerous advantages of these hydrogels over conventional drug delivery systems and find applications in various fields, such as therapeutic systems, filling processes, and sustained drug delivery systems. One of their key benefits is the ability to eliminate invasive procedures like surgery, providing a noninvasive alternative for drug administration. Moreover, they streamline the formulation process for both hydrophilic and hydrophobic drug delivery systems, simplifying the development of effective treatments. The thermosensitive hydrogels have been found to be green materials with negligible side effects and desirable drug delivery properties. The thermosensitive hydrogel's sustained‐release characteristics, immunogenicity, and biodegradability have also gained increased interest. Some of the disadvantages of thermosensitive hydrogels include delayed temperature response, weak mechanical characteristics, and poor biocompatibility, which limits their potential use in drug delivery applications.

Biomedicine is constantly evolving to ensure a significant and positive impact on healthcare, which has resulted in innovative and distinct requisites such as hydrogels. Chitosan-based formulations stand out for their versatile utilization in drug encapsulation, transport, and controlled release, which is complemented by their biocompatibility, biodegradability, and non-immunogenic nature. Stimuli-responsive hydrogels, also known as smart hydrogels, have strictly regulated release patterns since they respond and adapt based on various external stimuli. Moreover, they can imitate the intrinsic tissues’ mechanical, biological, and physicochemical properties. These characteristics allow stimuli-responsive hydrogels to provide cutting-edge, effective, and safe treatment. Constant progress in the field necessitates an up-to-date summary of current trends and breakthroughs in the biomedical application of stimuli-responsive chitosan-based hydrogels, which was the aim of this review. General data about hydrogels sensitive to ions, pH, redox potential, light, electric field, temperature, and magnetic field are recapitulated. Additionally, formulations responsive to multiple stimuli are mentioned. Focusing on chitosan-based smart hydrogels, their multifaceted utilization was thoroughly described. The vast application spectrum encompasses neurological disorders, tumors, wound healing, and dermal infections. Available data on smart chitosan hydrogels strongly support the idea that current approaches and developing novel solutions are worth improving. The present paper constitutes a valuable resource for researchers and practitioners in the currently evolving field.

Yi Sun,1,* Le-Gao Chen,2,* Xiao-Ming Fan,3 Jian-Liang Pang4 1Center for Plastic & Reconstructive Surgery, Department of Plastic & Reconstructive Surgery, Zhejiang Provincial People’s Hospital (Affiliated People’s Hospital, Hangzhou Medical College), Hangzhou, 310014, People’s Republic of China; 2General Surgery, Cancer Center, Department of Vascular Surgery, Zhejiang Provincial People’s Hospital (Affiliated People’s Hospital, Hangzhou Medical College), Hangzhou, 310014, People’s Republic of China; 3Cancer Center, Department of Ultrasound Medicine, Zhejiang Provincial People’s Hospital (Affiliated People’s Hospital, Hangzhou Medical College), Hangzhou, 310014, People’s Republic of China; 4Department of Vascular Surgery, Tiantai People’s Hospital of Zhejiang Province (Tiantai Branch of Zhejiang People’s Hospital), Taizhou, 317200, People’s Republic of China*These authors contributed equally to this workCorrespondence: Xiao-Ming Fan, Department of Ultrasound Medicine, Zhejiang Provincial People’s Hospital (Affiliated People’s Hospital, Hangzhou Medical College), No. 158 Shangtang Road, Hangzhou, Zhejiang, 310014, People’s Republic of China, Tel/Fax +86-571-85893290, Email fan-xiaoming@163.com Jian-Liang Pang, Department of Vascular Surgery, Tiantai People’s Hospital of Zhejiang Province (Tiantai Branch of Zhejiang People’s Hospital), Kangning Middle Road, Shifeng Street, Tiantai County, Taizhou, Zhejiang, 317200, People’s Republic of China, Tel/Fax +86-576- 81302085, Email ttzjpjl1982@163.comAbstract: Over the last two decades, the process of delivering therapeutic drugs to a patient with a controlled release profile has been a significant focus of drug delivery research. Scientists have given tremendous attention to ultrasound-responsive hydrogels for several decades. These smart nanosystems are more applicable than other stimuli-responsive drug delivery vehicles (ie UV-, pH- and thermal-, responsive materials) because they enable more efficient targeted treatment via relatively non-invasive means. Ultrasound (US) is capable of safely transporting energy through opaque and complex media with minimal loss of energy. It is capable of being localized to smaller regions and coupled to systems operating at various time scales. However, the properties enabling the US to propagate effectively in materials also make it very difficult to transform acoustic energy into other forms that may be used. Recent research from a variety of domains has attempted to deal with this issue, proving that ultrasonic effects can be used to control chemical and physical systems with remarkable specificity. By obviating the need for multiple intravenous injections, implantable US responsive hydrogel systems can enhance the quality of life for patients who undergo treatment with a varied dosage regimen. Ideally, the ease of self-dosing in these systems would lead to increased patient compliance with a particular therapy as well. However, excessive literature has been reported based on implanted US responsive hydrogel in various fields, but there is no comprehensive review article showing the strategies to control drug delivery profile. So, this review was aimed at discussing the current strategies for controlling and targeting drug delivery profiles using implantable hydrogel systems.Graphical Abstract: Keywords: smart hydrogels, ultrasound, acoustic energy, cavitation, on-demand drug delivery, localized therapy

Building long-lasting antimicrobial and clean surfaces is one of the most effective strategies to inhibit bacterial infection, but obtaining an ideal smart surface with highly efficient, controllable, and regenerative properties still encounters many challenges. Herein, we fabricate an ultrathin brush–hydrogel hybrid coating (PSBMA-P(HEAA-co-METAC)) by integrating antifouling polyzwitterionic (PSBMA) brushes and antimicrobial polycationic (P(HEAA-co-METAC)) hydrogels. The smart bacterial killing–releasing properties can be achieved independently by the opposite volume and conformation changes between the swelling (shrinking) of P(HEAA-co-METAC) hydrogel layer and the shrinking (swelling) of PSBMA brushes. The friction test reveals that both METAC and SBMA components support great lubrication. By tuning the initial organosilane (BrTMOS:KH570) ratios, the prepared PSBMA-P(HEAA-co-METAC) coating exhibits different antibacterial abilities from single “capturing–killing” to versatile “capturing–killing–releasing.” Most importantly, 99% of the bacterial-releasing rate can be easily achieved via 0.5 M NaCl treatment. This smart surface not only possesses long-lasting antibacterial performance, only ∼1.09 × 105 cell·cm−2 bacterial residue even after 72 h exposure to bacteria solutions, but also can be regenerated and triggered between water and salt solution multiple times. This work provides a new way to fabricate antibacterial smart hydrogel coatings with bacterial “killing–releasing” functions and shows great potential for biomedical applications.

A review of the literature on chemically responsive hydrogels about the selection of selectivity based on classification, properties, and application is presented in this article. Chemically responsive hydrogels are a type of hydrogel that undergo changes in their properties in response to specific stimuli. These hydrogels have attracted significant attention due to their potential applications in various fields, including pharmaceuticals and agriculture. Chemically crosslinked hydrogels are synthesized by covalent crosslinking of end-functionalized macromeres. Currently, a great deal of research is being conducted on hydrogel networks, also known as smart networks or hungry networks. This is owing to their potential use in fields like biomedicine, pharmaceuticals, biotechnology, biosensors, agriculture, oil recovery, and cosmetics. When they sense small changes in their surroundings, smart hydrogels display significant physiochemical changes. Despite this, changes such as these are reversible; therefore, the hydrogels can return to their original state after they have caused a reaction once the trigger has been removed. [ABSTRACT FROM AUTHOR]

Wound management represents a continuous challenge for health systems worldwide, considering the growing incidence of wound-related comorbidities, such as diabetes, high blood pressure, obesity, and autoimmune diseases. In this context, hydrogels are considered viable options since they mimic the skin structure and promote autolysis and growth factor synthesis. Unfortunately, hydrogels are associated with several drawbacks, such as low mechanical strength and the potential toxicity of byproducts released after crosslinking reactions. To overcome these aspects, in this study new smart chitosan (CS)-based hydrogels were developed, using oxidized chitosan (oxCS) and hyaluronic acid (oxHA) as nontoxic crosslinkers. Three active product ingredients (APIs) (fusidic acid, allantoin, and coenzyme Q10), with proven biological effects, were considered for inclusion in the 3D polymer matrix. Therefore, six API-CS-oxCS/oxHA hydrogels were obtained. The presence of dynamic imino bonds in the hydrogels' structure, which supports their self-healing and self-adapting properties, was confirmed by spectral methods. The hydrogels were characterized by SEM, swelling degree, pH, and the internal organization of the 3D matrix was studied by rheological behavior. Moreover, the cytotoxicity degree and the antimicrobial effects were also investigated. In conclusion, the developed API-CS-oxCS/oxHA hydrogels have real potential as smart materials in wound management, based on their self-healing and self-adapting properties, as well as on the benefits of APIs. [ABSTRACT FROM AUTHOR]

The present endeavor is to develop a highly-intelligent catalytic reactor prototype which is able to autonomously adapt to the environment and provides an in-situ double-shift catalytic ability. By seeking inspiration from nature, this objective is achieved by developing a self-adaptive hydrogel catalytic reactor which held a catalytic trilaminar structure capable of reverse thermosensitive properties. With increasing temperatures, the catalytic tri-layers of this catalytic reactor would function in a sequential way (i.e., one negative temperature response layer, one support layer and one positive temperature response layer) and as a result, led to the single-tandem double-shift catalytic ability. This catalytic reactor individually presented single/tandem catalytic process at relatively low temperatures or high temperatures through the cooperative work of the three layers. In this way, this catalytic reactor showed the single-tandem controllable catalytic ability. The novel protocol not only provides a new solution to complicated catalytic processes but also inspires the further application of smart polymers in a broader spectrum of areas. [ABSTRACT FROM AUTHOR]

Modified P(NIPAm-co-AAc) copolymers are prepared using Radical Addition Fragmentation Chain Transfer (RAFT) copolymerization by varying the concentration of castor oil sourced acrylated epoxy methyl ricinoleate (AEMR). Subsequently, hydrogels are prepared by integrating copolymers with polyvinyl alcohol (PVA) via freeze-thaw process. The employment of RAFT polymerization yielded copolymers with dispersity (D) value of 1.2–1.3 revealing the formation of structurally well controlled polymer chains. The lower critical solution temperature (LCST) of the copolymers (∼30–35 °C) are tuned to the range of physiological temperature (∼37 °C) in PVA hydrogel system. Temperature dependent viscoelastic properties indicated that the characteristics of copolymeric solutions and hydrogels are composition dependent while undergoing noncovalent interactions and the conformational changes and the samples showed extremely elastic behaviour beyond LCST. Swelling ratio of hydrogels are also found to be pH dependent, which displayed higher swelling ratio in alkaline and reduced swelling ratio in acidic medium. Cytotoxicity studies with L929 cells showed that the copolymers and hydrogels exhibited desirable biocompatibility, which gets improved with AEMR concentrations. Thus, these dual responsive PA-AEMR-PVA smart hydrogels can be used as a viable functional material for possible bio-medical applications. [Display omitted] • Bio-based temperature and pH responsive NIPAm co-polymers were prepared via RAFT polymerization. • Co-polymers demonstrated well-defined structure with a Dispersity (D) value of 1.1–1.3. • The co-polymer, with poly vinyl alcohol (PVA), was used to prepare smart hydrogels through freeze-thawing technique. • Hydrogels are bio-compatible towards L929 cells with increase in AEMR content. [ABSTRACT FROM AUTHOR]

Objective(s): Recently, great attention has been paid to developing new drug delivery systems to manage the rate, time, and site of drug release. We aimed to design a novel drug delivery system to support targeted and gradual delivery of levothyroxine sodium.Materials and Methods: The triblock copolymers of PLA-PEG-PLA and PLGA-PEG-PLGA were constructed using the ring-opening copolymerization method and then purified and characterized by 1H-NMR, DSC, and GPC techniques. The phase transition temperature of the polymers was determined, and levothyroxine sodium stability was investigated in a phosphate-based buffer (pH 7.4). In vitro drug release into the PBS was measured at different concentrations of the triblocks for one month. Results: The results of NMR and GPC showed successful fabrication of the copolymers with low molecular weight dispersion and Tg points of -8.19 °C and -5.19 °C for PLA-PEG-PLA and PLGA-PEG-PLGA, respectively. Stability tests showed that during one month, most of the triblocks’ masses degraded at 37 °C while levothyroxine sodium remained stable. Initial burst release of the drug in both copolymers is inversely correlated with the concentration of the polymer. Evaluation of drug release for 35 days showed that PLA-PEG-PLA had a slower drug release rate than PLGA-PEG-PLGA.Conclusion: Considering the low initial burst release, as well as continuous and long-term release kinetics of PLA-PEG-PLA and PLGA-PEG-PLGA copolymers, they can be used to gradually deliver levothyroxine sodium, obviating the need for frequent administrations and concerns over drug-food interactions.

Novel double cross-linked (DC) hydrogels with pH-/temperature-sensitive properties were designed and developed. Therefore, linear pH-sensitive poly(methyl vinyl ether-alt-maleic acid) (P(VME/MA)) macromolecules were absorbed within a thermosensitive poly(N-isopropylacrylamide-co-hydroxyethylacrylamide)-hydrogel (PNH) and, subsequently, cross-linked together through a solvent-free thermal method. As a novelty, double cross-linked hydrogels were obtained from previously purified polymers in the absence of any solvent or cross-linking agent, which are generally harmful for the body. The new DC structures were characterized by FT–IR spectroscopy, SEM, swelling kinetic measurements, and mechanical tests. The resulting scaffolds exhibited interconnected pores and a flexible pattern, compared to the brittle structure of conventional PNH. The swelling kinetics of DC hydrogels were deeply affected by temperature (25 and 37 °C) and pH (7.4 and 1.2). Furthermore, the hydrogels absorbed a great amount of water in a basic environment and displayed improved mechanical properties. Metoclopramide (Met) was loaded within DC hydrogels as a model drug to investigate the ability of the support to control the drug release rate. The results obtained recommended them as convenient platforms for the oral administration of drugs, with the release of the largest part of the active principle occurring in the colon. [ABSTRACT FROM AUTHOR]

This review aims at giving selected chemical and mechanical insights on design criteria that should be taken into account in hydrogel production for biomedical applications. Particular emphasis will be given to the chemical aspects involved in hydrogel design: macromer chemical composition, cross‐linking strategies and chemistry towards "conventional" and smart/stimuli responsive hydrogels. Mechanical properties of hydrogels in view of regenerative medicine applications will also be considered. [ABSTRACT FROM AUTHOR]

Hydrogel-based flexible electronic components have become the optimal solution to address the rigidity problem of traditional electronics in health management. In this study, a multipurpose hydrogel is introduced, which is formed by combining a dual-network consisting of physical (chitosan, polyvinyl alcohol (PVA)) and chemical (poly(isopropyl acrylamide (NIPAM)-co-acrylamide (AM))) cross-linking, along with signal conversion fillers (eutectic gallium indium (EGaIn), Ti 3 C 2 MXene, polyaniline (PANI)) for responding to external stimuli. Multiple sensing of dynamic and static signals is permissible for it. The strain sensor based on the hydrogel exhibits up to a 1000% resistance change within a 400% stretch range, and significant capacitance variations are observed upon touch. The temperature sensor yields a sensitivity of ≈-2.9% °C -1 at 20-40 °C and ≈65% °C -1 at 0-20 °C. The pH sensor responds with a sensitivity of near -13.68 mV pH -1 . A paper-based triboelectric nanogenerator can be assembled to collect action energy at 83 mW m -2 . The skin contact interface is kept in good condition owing to its 3D-printability, controllable antibacterial properties, along high cell survival rate. This multifunctional hydrogel holds promise in facilitating the integration of diagnosis and maintenance., (© 2024 Wiley‐VCH GmbH.)

Materials with excellent biocompatibility and targeting can be widely used in the biomedical field. Hydrogels are an excellent biomedical material, which are similar to living tissue and cannot affect the metabolic process of living organisms. Moreover, the three-dimensional network structure of hydrogel is conducive to the storage and slow release of drugs. Compared to the traditional hydrogel preparation technologies, ionizing radiation technology has high efficiency, is green, and has environmental protection. This technology can easily adjust mechanical properties, swelling, and so on. This review provides a classification of hydrogels and different preparation methods and highlights the advantages of ionizing radiation technology in smart hydrogels used for biomedical applications. [ABSTRACT FROM AUTHOR]

Advancements in the material design of smart hydrogels have transformed the way therapeutic agents are encapsulated and released in biological environments. On the other hand, the expeditious development of 3D printing technologies has revolutionized the fabrication of hydrogel systems for biomedical applications. By combining these two aspects, 4D printing (i.e., 3D printing of smart hydrogels) has emerged as a new promising platform for the development of novel controlled drug delivery systems that can adapt and mimic natural physio-mechanical changes over time. This allows printed objects to transform from static to dynamic in response to various physiological and chemical interactions, meeting the needs of the healthcare industry. In this review, we provide an overview of innovation in material design for smart hydrogel systems, current technical approaches toward 4D printing, and emerging 4D printed novel structures for drug delivery applications. Finally, we discuss the existing challenges in 4D printing hydrogels for drug delivery and their prospects. [ABSTRACT FROM AUTHOR]

Smart hydrogels based on natural polymers present an opportunity to fabricate responsive scaffolds that provide an immediate and reversible reaction to a given stimulus. Modulation of mechanical characteristics is especially interesting in myocyte cultivation, and can be achieved by magnetically controlled stiffening. Here, hyaluronan hydrogels with carbonyl iron particles as a magnetic filler are prepared in a low-toxicity process. Desired mechanical behaviour is achieved using a combination of two cross-linking routes—dynamic Schiff base linkages and ionic cross-linking. We found that gelation time is greatly affected by polymer chain conformation. This factor can surpass the influence of the number of reactive sites, shortening gelation from 5 h to 20 min. Ionic cross-linking efficiency increased with the number of carboxyl groups and led to the storage modulus reaching 10 3 Pa compared to 10 1 Pa–10 2 Pa for gels cross-linked with only Schiff bases. Furthermore, the ability of magnetic particles to induce significant stiffening of the hydrogel through the magnetorheological effect is confirmed, as a 10 3 -times higher storage modulus is achieved in an external magnetic field of 842 kA·m − 1 . Finally, cytotoxicity testing confirms the ability to produce hydrogels that provide over 75% relative cell viability. Therefore, dual cross-linked hyaluronan-based magneto-responsive hydrogels present a potential material for on-demand mechanically tunable scaffolds usable in myocyte cultivation. [ABSTRACT FROM AUTHOR]

[Display omitted] Smart hydrogels with good flexibility and biocompatibility have been widely used. The common near-infrared (NIR) photothermal agents are facing a trade-off between good photothermal-conversion efficiency and high biocompatibility. Therefore, developing new metal-free photothermal agents with low cost, high biocompatibility and excellent phase stability is still in urgent need. In this study, we successfully combined poly(N -isopropylacrylamide) (PNIPAM) with the two-dimensional (2D) silicene nanosheets via the in situ polymerization method. Attributed to the thermal-responsive nature of PNIPAM and the excellent photothermal properties of 2D silicene, the obtained silicene/PNIPAM composite hydrogels exhibited dual thermal and NIR responsive properties. This smart hydrogel showed rapid, reversible and repeatable NIR light-responsive behaviors. The volume of this smart hydrogels can shrink significantly under NIR irradiation and recover to its original size without the NIR irradiation. Remote near-infrared light-controlled microfluidic pipelines and electronic switches based on obtained silicene/PNIPAM composite hydrogels were also demonstrated. This work significantly broadens the application prospects of silicene-based hydrogels in remote light-controlled devices. [ABSTRACT FROM AUTHOR]

Stimuli-responsive hydrogel drug delivery systems are designed to release a payload when prompted by an external stimulus. These platforms have become prominent in the field of drug delivery due to their ability to provide spatial and temporal control for drug release. Among the different external triggers that have been used, ultrasound possesses several advantages: it is non-invasive, has deep tissue penetration, and can safely transmit acoustic energy to a localized area. This review summarizes the current state of understanding about ultrasound-responsive hydrogels used for drug delivery. The mechanisms of inducing payload release and activation using ultrasound are examined, along with the latest innovative formulations and hydrogel design strategies. We also report on the most recent applications leveraging ultrasound activation for both cancer treatment and tissue engineering. Finally, the future perspectives offered by ultrasound-sensitive hydrogels are discussed. [ABSTRACT FROM AUTHOR]

The latest research progress of smart hydrogels, such as temperature-responsive, pH-responsive, redox-responsive, enzyme-responsive and multiple-responsive hydrogels, in drug therapy, gene therapy and protein therapy was reviewed. Suggestions were put forward to improve the shortcomings of smart hydrogels such as sudden release effect, biocompatibility and biodegradability in clinic. [ABSTRACT FROM AUTHOR]

Wearable bioelectronics and therapeutics are a rapidly evolving area of research, with researchers exploring new materials that offer greater flexibility and sophistication. Conductive hydrogels have emerged as a promising material due to their tunable electrical properties, flexible mechanical properties, high elasticity, stretchability, excellent biocompatibility, and responsiveness to stimuli. This review presents an overview of recent breakthroughs in conductive hydrogels, including their materials, classification, and applications. By providing a comprehensive review of current research, this paper aims to equip researchers with a deeper understanding of conductive hydrogels and inspire new design approaches for various healthcare applications.

Hydrogels are among the most promising materials for biological applications mainly because of their ability to absorb large volumes of water and carry as well as deliver biologically active substances. A challenge is to make them appropriately responsive to environmental triggering factors simply and reliably. In this work, we present a basic approach of modification of a commonly used, low-cost poly (acrylic acid) – PAA – hydrogel with biocompatible surfactants regarding their possible thermoresponsive activity.Viscoelasticity, hydration, and molecular diffusion processes, in relation to the morphology of the hydrogel and its mixture with nonionic surfactant Brij 58, are studied systematically using oscillatory rheometry, NMR diffusiometry and imaging, and cryoSEM. Our results contribute to the understanding of interactions between weak PAA and nonionic surfactants. The changes of the hydrogel microstructure caused by nonionic and bio-safe surfactant or thermal induction are clearly reflected in their mechanical response as well as the translational mobility of water molecules entrapped within the hydrogel's network. The structural modification induced by adding nonionic surfactant gives rise to a decrease in hydrogel elasticity. • The addition of nonionic surfactants makes hydrogels more thermoresponsive. • Complementary description of the relations between structure, mechanical properties, and molecular diffusion in modified hydrogels. • Nonionic surfactants interact strongly enough with poly(acrylic acid) to alter micro and macroscopic features remarkably. • Efficient drug delivery systems can be potentially created by limiting and controlling diffusion in weakly crosslinked and well-hydrated hydrogels by easy and safe modifications. [ABSTRACT FROM AUTHOR]

Hydrogels are significant hydrophilic materials with 3D polymeric network structures, which have received much attention in recent decades. DNA-based hydrogel materials have been widely used for tissue engineering, biosensors, bioanalysis, and clinical therapy on their excellent stability, bioanalysis, biocompatibility, and programmability. The addition of functional DNA (deoxyribonucleic acid) sequences, such as DNAzymes or aptamers, are embedded in polymer networks, which expand the additional molecular recognition capabilities and sensibility of smart DNA hydrogels. In particular, targeting-responsive DNA hydrogels have attracted much attention and provided a portable, sensitive, selective, and visualised detection platform for biosensors. In this review, the latest applications of distinct types of DNA hydrogel biosensors for detection in various fields are introduced. Then, the prospects for future development trends and challenges of DNA-based hydrogel materials for biosensing are given. [ABSTRACT FROM AUTHOR]

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Bone defects, as one of the most urgent problems in the orthopedic clinic, have attracted much attention from the biomedical community and society. Hydrogels have been widely used in the biomedical field for tissue engineering research because of their excellent hydrophilicity, biocompatibility, and degradability. Stimulus-responsive hydrogels, as a new type of smart biomaterial, have more advantages in sensing external physical (light, temperature, pressure, electric field, magnetic field, etc.), chemical (pH, redox reaction, ions, etc.), biochemical (glucose, enzymes, etc.) and other different stimuli. They can respond to stimuli such as the characteristics of the 3D shape and solid–liquid phase state, and exhibit special properties (injection ability, self-repair, shape memory, etc.), thus becoming an ideal material to provide cell adhesion, proliferation, and differentiation, and achieve precise bone defect repair. This review is focused on the classification, design concepts, and research progress of stimulus-responsive hydrogels based on different types of external environmental stimuli, aiming at introducing new ideas and methods for repairing complex bone defects. [ABSTRACT FROM AUTHOR]